Structures having two vibrating masses mechanically coupled in the manner of a tuning fork have already been produced: the structure of a gyroscope thus produced typically comprises two coplanar moving assemblies excited so as to vibrate and connected in the manner of a tuning fork, that is to say the two assemblies are connected to a central coupling structure that transfers the vibration energy of the first assembly to the second assembly, and vice versa. The assemblies are excited into vibration in the plane of the wafer by an electrical excitation structure. This vibration in the plane of the wafer is exerted perpendicularly to an axis, called the sensitive axis, of the gyroscope, perpendicular to the direction of this vibration. When the gyroscope rotates at a certain angular velocity about its sensitive axis, the composition of the forced vibration with the angular rotation vector generates, by the Coriolis effect, forces that set the moving assemblies into natural vibration perpendicular to the excitation vibration and to the rotation axis. The amplitude of this natural vibration is proportional to the rotation rate. The natural vibration is detected by an electrical detection structure. The resulting electrical signals are used to deduce therefrom the angular velocity about the sensitive axis.
Patent applications FR 2 846 740 and FR 2 859 527 disclose gyroscopes in which the sensitive axis is the Oz axis perpendicular to the plane of the moving masses. The excitation movement of the moving assemblies is generated along a direction Ox of the plane whereas movement resulting from the Coriolis force is detected in a direction Oy of the same plane, perpendicular to Ox.
Patent application FR 2 846 740 discloses a gyroscope of the type having a tuning-fork architecture. Each moving assembly of this gyroscope comprises an inertial first moving element connected to the coupling structure and able to vibrate with two degrees of freedom in orthogonal directions Ox and Oy of the plane of the wafer, and a second moving element connected on one side to the first moving element and on the other side to fixed anchoring zones via linkage means that allow the vibration movement of the first element along the Oy direction to be transmitted to the second element without allowing the second element to move along the Ox direction.
The tuning fork architecture has a drawback, namely detection mode in which the moving elements of a moving assembly vibrate along the Oy direction is not dynamically balanced. This is because the two moving elements vibrate in phase opposition in the Oy direction. Consequently, this mode transmits a torque to the support of the tuning fork, making this mode sensitive to the conditions of attachment to the support and sensitive to the external perturbations transmitted by the support.
To remedy this problem, a double tuning-fork solution disclosed in patent application FR 2 859 527 is known. Each moving assembly of this gyroscope comprises three moving elements, an inertial first moving element connected to the coupling structure and intended to vibrate along two orthogonal directions Ox and Oy in the plane of the wafer, a second moving element intended to vibrate along Oy and connected to the first moving element and to fixed anchoring zones via linkage means that allow the vibration movement of the first moving element along Oy to be transmitted to the second moving element without allowing the second element to move along the Ox direction, and a third moving element intended to vibrate along Oy and connected to the second moving element and to fixed anchoring zones via second linkage means that allow transmission, in phase opposition, of the vibration movement of the second moving element along Oy to third moving element.
What is thus obtained is a double tuning-fork gyroscope having a balanced detection movement within each of the moving assemblies because the movement of the third moving element counterbalances the movement of the first and second moving elements. A rotation rate is measured with very great sensitivity, as in the case of a single tuning fork, and with minimal perturbations due to the excitation movement.
However, the double tuning-fork gyroscope of the prior art has the drawback, owing to the addition of an additional moving element in each moving assembly, of being larger in size and therefore more costly and more complicated to produce than a single tuning fork.
This drawback is exacerbated by the fact that the addition of the third moving element adds parasitic vibration modes having, because of etching defects, frequencies that are much more difficult to bring under control than with a simple tuning fork.